Almost everything can be grilled. Even fruit. The key is to coat items with olive oil and enough salt and pepper to bring out the flavor.  Try not to blacken the veggies.  Like roasting, the water and sugar content in the vegetables determine how long they will take to grill. You’ll get a feel for it over time, and you’ll know to chop some things bigger and some smaller so they cook evenly together.

Ingredients
Anything you can think of, even whole heads of romaine lettuce
olive oil
Salt
Pepper
Herbs and spices (optional)

Instructions
Heat up the grill to medium high
Chop veggies and coat with olive oil, salt, pepper and any spices and herbs
Place vegetables directly on grill, or thread them on skewers
Try and cook to tender-crisp, which means soft but still crunchy

Advanced tip 1: Make more than you need and add leftover veggies to salads and pasta dishes later in the week.

Advanced tip 2: Avocados can be grilled. (cut in half, brush with olive oil, leave skin on) So can peaches. (same, or cut into slices) Grilled peaches on a salad with chicken is really good in summer.